Unit 2 Flashcards
Describe light as a wave
Light is electromagnetic radiation, consisting of an oscillating electric field and magnetic field (waves)
What is 3.0 x 10^8 m/s
The speed of light
What determines colour?
Wavelength
As the wavelength size becomes smaller (moves further right on the spectrum), does energy increase or decrease?
More energy is carried with a smaller wavelength (further on the spectrum)
What is a blackbody?
A theoretical object that that absorbs ALL radiation hitting it and is a perfect emitter of EM
What does Wien’s displacement tell us?
The Max wavelength of an object is inversely proportional to temperature: Smaller wavelengths have more energy and therefore are hotter (blue)
What does Wien’s law tell us about solar vs terrestrial radiation?
The peak of solar radiation is around 500 nm in the visible range, terrestrial radiation is in the infrared and therefore is not visible to us
Compare Active and Passive remote sensing
Active includes sensors that have their own energy (LIDAR)
Passive relies on energy from a different source like reflective from the sun
What are the two kinds of reflectance?
Specular or Mirror-like Reflectance (smooth surfaces)
Diffuse Reflection (rough surfaces)
Why does water show up black when using near-infrared in Landsat imagery?
Water’s spectral reflectance signature is only present in the Blue, Green, and Red part of the spectrum (absorbs other wavelengths)
Are real-world surfaces Lambertian?
No, most surfaces are non-Lambertian. They do not reflect light equally in all directions.
What is the Bidirectional Reflectance Function (BDRF)?
The consideration of the direction of incidence radiation as well as the viewing direction. The differences in angle change the amount of energy being detected.
When does a “hot spot” occur?
When the viewing angle is the same as the angle of the sun.
What phenomenon of BDRF is the result of specular reflection?
Sun Glint
When does atmospheric scattering occur?
Radiation is redirected out of the incident path but the wavelength of the scattered light doesn’t change.
How do O2, N2, water vapour, and other molecules or aerosols affect light?
They scatter light into the path of sensors or away from the sensors
Which particle size is associated with Rayleigh scattering?
smaller than wavelength (ex. gas molecule) = blue/violet part of spectrum
What is Mie Scattering?
When the size of the particle is about the same size of the wavelength (ex. smoke or dust) = red & orange part of spectrum
If the particle is much larger than the wavelength what occurs?
Non-selective scattering (ex. water vapour) = no strong colour as all equally scattered
Why can you still see details in a picture of a shadow?
Scattering of light into sensor path
What are transmission and transmittance?
The passing of light through a medium
The proportion of light allowed to pass through the medium
What happens when light is absorbed by a material?
It can be converted to other forms of energy (ie. thermal) = no longer available to sensors
How can we use absorption to determine what is in the atmosphere?
We can analyze absorption bands at specific wavelengths to see what is doing the absorbing
How is fluorescence different from absorption?
Causes excitation of an e- to elevate it to a higher energy level, when it drops to steady-state it emits EM
How can we apply fluorescence in remote sensing?
Greater amounts of chlorophyll relate to higher fluorescence which can help to monitor photosynthetic activity and therefore carbon sequestration
what is a forward model?
simulates light returned to a sensor given known properties of the atmosphere and earth’s surface
What is an inversion model?
Determine properties of atmosphere or earth’s surface given a known reflected signal
